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| DS2109 DS2109 Plug and Play SCSI Terminator FEATURES PIN ASSIGNMENT PDI R1 R2 R3 R4 R5 HS-GND HS-GND PDO R6 R7 R8 R9 TPWR 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 GND R18 R17 R16 R15 R14 TCS HS-GND PDE R13 R12 R11 R10 VREF * Fully SCSI compliant with SCSI-1, Fast SCSI and Ultra * Compatible with Plug and Play SCSI Profile * Functionally compatible with DS21S07A * Provides active termination for 18 signal lines * 2% tolerance on termination resistors and voltage regulator * Bus termination sensing * Low power down capacitance of 3 pF * Onboard thermal shutdown circuitry DS2109, DS2109S 28-PIN SOIC (300 MIL) DESCRIPTION The DS2109 is intended for one chip Plug and Play (PnP) SCSI termination. Plug and Play SCSI requires the exit-point terminator on computer motherboards or host bus adapters to automatically switch off if an external device is connected to the system. The DS2109 satisfies this requirement by offering the engineer a choice of onboard current sensing circuitry or onboard ground detect circuitry. If an external device is connected, the DS2109 will automatically be isolated from the SCSI bus thereby maintaining proper system termination. The DS2109 integrates a low drop-out regulator, 18 precise switched 110 ohm termination resistors, and bus termination sensors into a 28-pin 300 mil SOIC package. Active termination provides: greater immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2109 contains an output port that can control the power down pin of additional terminators (DS21S07A) for Wide SCSI applications. 022698 1/10 DS2109 REFERENCE DOCUMENTS SCSI-2 (X3.131-1994) SCSI-3 Parallel Interface (X3T10/855D) Available from: Global Engineering Documents 15 Inverness Way East Englewood, CO 80112-5704 Phone: (800) 854-7179,(303) 792-2181 Fax: (303) 792-2192 PnP SCSI Specification PnP ISA Specification PnP BIOS Specification PnP Option ROM Specification Available from: Plug and Play forum on CompuServe (Go plugplay). FUNCTIONAL DESCRIPTION The DS2109 is designed to be a single chip termination subsystem for use in PnP SCSI systems, Figure 1. When embedded on a host bus adapter or motherboard, the DS2109 can automatically sense the termination status of the SCSI bus and attach or isolate its resistors as needed to maintain proper bus termination. External and internal active termination can be provided by the DS21S07A. DS2109 APPLICATION ENVIRONMENT Figure 1 PERIPHERAL SUBSYSTEM DS2109 AUTOMATIC EXIT-POINT TERMINATOR EXTERNAL TERMINATOR (TWO DS21S07A) 50-POSITION HIGH DENSITY CONNECTORS HOST SCSI PROTOCOL CHIP SCSI EXTERNAL CABLE SCSI PERIPHERAL DEVICES SCSI INTERNAL CABLES INTERNAL TERMINATOR (TWO DS21S07A) 022698 2/10 DS2109 The DS2109 consists of 3 major functional blocks, Figure 2: * Voltage reference, terminating resistors, and isolation switches * Bus current sensing circuitry * Bus ground sensing circuity When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determine that the SCSI bus is prop- erly terminated without the DS2109, the power down buffer isolates the resistors from the SCSI bus and disables the power amp, thereby placing the DS2109 in a low power mode (the bus sensing circuitry always stays active). The PDO (Power Down Output) pin can be connected to the pin of a DS21S07A SCSI terminator for Wide SCSI configurations, Figure 8. DS2109 BLOCK DIAGRAM Figure 2 PDI BUS GROUND SENSING CIRCUITRY DISABLE DISABLE BUS CURRENT SENSING CIRCUITRY TCS PDE PDO POWER DOWN BUFFER BANDGAP REFERENCE + 110 OHMS R14 - 110 OHMS R18 110 OHMS R1 VREF 022698 3/10 DS2109 DETAILED PIN DESCRIPTION Table 1 PIN 1 2-6, 10-13, 16-19, 24-27 7, 8, 21 9 14 15 20 22 SYMBOL PDI R1...R13 R15...18 FCN I T DESCRIPTION Power Down Internal. For Bus Ground Sensing Circuit connect to pin 22 of internal SCSI connector, see Figure 4. Signal Termination. 110 ohm termination. Connect to SCSI bus signal lines. For Bus Current Sensing Circuit connect to data, parity, and control lines, except SCSI-RST line, see Figure 6. Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electronically isolated from other circuitry. Power Down Output. Connect to DS21S07A for Wide SCSI applications, see Figure 8. Termination Power. Connect to the SCSI TERMPWR line. Bypass with a 2.2 F capacitor, see Figures 4 and 6. Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7 F capacitor, see Figures 4 and 6. Power Down External. For Bus Ground Sensing Circuit, connect to pin 36 of external SCSI connector, see Figure 4. Termination Current Sense. Used to sense current on the SCSI bus. For Bus Current Sensing Circuit, connect to SCSI signal line -RST, see Figure 6. Signal Termination. 110 ohm termination. Connect to SCSI bus signal line. For Bus Current Sensing Circuit connect to SCSI controller chip, see Figure 6. Ground. Signal ground; 0.0 volts. As with all analog circuitry, the TERMPWR lines should be bypassed locally. A 2.2 F capacitor is recommended between TPWR and ground and placed as close as possible to the DS2109. The DS2109 should be placed as close as possible to the connector to minimize signal and power trace length, thereby resulting in less input capacitance and reflections which can degrade the bus signals. HS-GND PDO TPWR VREF PDE TCS P O P O I I 23 R14 T 28 GND P ACTIVE TERMINATION The voltage regulator circuitry (bandgap reference and class AB power amplifier) produces a precise laser- trimmed 2.85 volt level and is capable of sourcing 24 mA into each of the terminating resistors when the signal line is low (active). When the external driver for a given signal line turns off, the active terminator will pull that signal line to 2.85 volts (quiescent state). When used with an active negation driver, the power amp can sink 22 mA per line while keeping the voltage reference in regulation; the terminating resistors maintain their 110 value over the entire voltage range. To maintain the specified regulation, a 4.7 F capacitor is required between the VREF pin and ground. A high frequency cap (0.1 F ceramic recommended) can also be placed on the VREF pin in applications that use fast rise/fall time drivers. The power down capacitance on terminating resistors R1-R13 and R15-R18 is <4 pF; R14 is slightly higher due to the bus current sensing circuitry. The DS2109 can be removed from the SCSI bus by using either of two automatic methods, Bus Ground Sensing or Bus Current Sensing. BUS GROUND SENSING If internal and external SCSI devices are connected to the SCSI bus, the DS2109 will disconnect from the SCSI bus according to the circuit in Figure 3. To utilize this automatic disconnect method of bus sensing, configure the DS2109 as shown in Figure 4. The PDI (Power Down Internal) pin should be connected to pin 22 of the internal SCSI connector, and the PDE (Power Down External) connected to pin 36 of the external SCSI connector. 022698 4/10 DS2109 BUS GROUND SENSING CIRCUIT Figure 3 PDI DISABLE PDE BUS GROUND DETECT CONFIGURATION Figure 4 INTERNAL SCSI CONNECTOR 22 26 TERMPWR 2.2 F DS2109 38 36 PDE TPWR VREF 4.7 F EXTERNAL SCSI CONNECTOR 022698 5/10 PDI GND DS2109 BUS CURRENT SENSING The DS2109 has the capability to use current sensing to determine if the SCSI bus is over- or under-terminated. A series 1 ohm resistor between pads R14 and TCS is inserted into the SCSI bus (preferably the -RST line) and used to monitor the current when that line pulls low (active, or "asserted" state). Based on the current measured, the DS2109 will disconnect or connect from the SCSI bus. The configuration for this automatic isolation technique is shown in Figure 6. Figure 5 shows a simplified diagram of the sensing circuit. The voltage across the 1 ohm sense resistor is differentially amplified and converted into a single-ended voltage with respect to ground. This is fed into a bank of comparators and measured against a reference voltage. The circuit takes a measurement each time TCS is driven below a 0.8 volts threshold and the outputs are latched on the rising edge of TCS. If IBUS is greater than 32 mA, the DS2109 will be isolated from the SCSI bus. It is recommended that the signal on TCS be asserted for at least 25 msec to allow the signal (and comparator outputs) to settle into a known state. A timing diagram of the sensing and latching operation is shown in Figure 7. It is preferred that the -RST line be used for monitoring the bus termination status because -RST is only asserted during power up or during a major change in bus configuration. Note that R14 will have a higher input capacitance than the other lines because of the additional circuitry required for bus sensing. The DS2109 will be isolated from the SCSI bus as shown in Table 2. BUS CURRENT SENSING CIRCUITRY Figure 5 TO SCSI CONTROLLER FROM SCSI BUS (-RST) R14 1 OHM 110 OHM IBUS TCS -+ REF DECODE AND LATCH 022698 6/10 DS2109 BUS CURRENT SENSE CONFIGURATION Figure 6 INTERNAL SCSI CONNECTOR 26 40 TERMPWR 38 DS2109 TPWR 2.2 F R1 EXTERNAL SCSI CONTROLLER 45 TCS -RST R14 -RST SCSI CONTROLLER 25 s min R13 R15 VREF R18 4.7 F GND BUS CURRENT SENSE TIMING DIAGRAM Figure 7 TCS COMPARATORS LATCH 022698 7/10 DS2109 DISCONNECT MODES Table 2 PDI 0 0 1 1 0 0 1 1 PDE 0 1 0 1 0 1 0 1 IBUS > 32 mA? No No No No Yes Yes Yes Yes DS2109 ISOLATED FROM SCSI BUS? Isolated Connected Connected Connected Isolated Isolated Isolated Isolated NOTE: "1" denotes pin left open circuited. WIDE SCSI CONFIGURATION Figure 8 TERMINATION POWER LINE 2.2 F TERMPWR1 R1 R2 R3 R4 R5 VREF1 GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 PD VREF2 NC R9 R8 R7 R6 TERMPWR2 PDI R1 R2 R3 R4 R5 HS-GND HS-GND PDO R6 R7 R8 4.7 F R9 TPWR 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 GND R18 R17 R16 R15 R14 TCS HS-GND PDE R13 R12 R11 R10 VREF 4.7 F DS21S07A 16-PIN SOIC (300 MIL) DS2109S 28-PIN SOIC (300 MIL) 022698 8/10 DS2109 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -1.0V to +7.0V 0C to 70C -55C to +125C 260C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. RECOMMENDED OPERATING CONDITIONS PARAMETER TERMPWR Voltage Logic 1 Logic 0 SYMBOL VTP VIH VIL MIN 4.00 2.0 -0.3 TYP MAX 5.25 VTP+0.3 +0.8 UNITS V V V (0C to 70C) NOTES 1 1 DC CHARACTERISTICS PARAMETER TERMPWR Current Power Down Current Termination Resistance Die Thermal Shutdown Power Down Termination Capacitance Input Leakage High Input Leakage Low Output Current Bus Current Sense Trip Point SYMBOL ITP ITP IPD RTERM TSD CPD C14 IIH IIL IO IBCST 4 32 -1.0 1.0 108 MIN TYP 10 1 110 150 3 8 4.5 MAX 500 14 2 112 UNITS mA mA mA ohms C pF pF A A mA mA (0C to 70C) NOTES 2, 4 2, 5 2, 3, 6 2, 3 2 2, 3, 6, 7 2,3,6,7,8 2, 12 2, 9, 12 10 11 REGULATOR CHARACTERISTICS PARAMETER Output Voltage Drop Out Voltage Line Regulation Load Regulation Current Limit Sink Current SYMBOL VREF VDROP LIREG LOREG IL ISINK MIN 2.79 TYP 2.85 0.75 1.0 1.3 700 400 MAX 2.91 1.0 2.0 3.0 UNITS V V % % mA mA (0C to 70C) NOTES 2, 3 4, 7 2, 5 2, 3 2 2 022698 9/10 DS2109 NOTES: 1. PDI, PDE, TCS 2. 4.00V < TERMPWR < 5.25V. 3. 0.0V < signal lines < 3.0V. 4. All signal lines = 0.0V. 5. All signal lines open. 6. Power down enabled. 7. Guaranteed by design; not production tested. 8. C14 slightly higher capacitance due to sensing circuitry. 9. Excluding PDI, PDE pins. 10. PDO output pin. 11. IBCST > 32 mA - disable termination. 12. Excluding PDE, PDI, R14, and TCS pins. 28-PIN SOIC (300 MIL) PKG DIM A IN. MM A1 IN. MM A2 IN. MM b IN. MM C IN MM D IN. MM e IN. MM 28-PIN MIN 0.094 2.39 0.004 0.102 0.089 2.26 0.013 0.33 0.009 0.229 0.698 17.73 MAX 0.105 2.67 0.012 0.30 0.095 2.41 0.020 0.51 0.013 0.33 0.712 18.08 0.050 BSC 1.27 BSC 0.290 7.37 0.398 10.11 0.016 0.40 0 0.300 7.62 0.416 10.57 0.040 1.02 8 The chamfer on the body is optional. If it is not present, a terminal 1 identifier must be positioned so that 1/2 or more of its area is contained in the hatched zone. E1 IN. MM H IN MM L IN MM 022698 10/10 |
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